As a technique on a reclining device for seat for adjusting the inclination angle of a seat back, a reclining device is disclosed in, for example, Prior Art 1. This reclining device moves a plurality of lock gears which contact a cam radially and outwardly due to rotation of the cam so as to be guided by each guide protrusion of a base plate, thereby engaging an external tooth of each lock gear with an internal tooth of a gear plate. Thereby, the base plate fixed to a seat cushion and the gear plate fixed to the seat back are locked with respect to each other so as not to be rotatable. By adopting four lock gears, the number of the external teeth of the lock gears engaged with the internal teeth of the gear plate is increased to enhance the locking strength between the base plate and the gear plate.
[Prior Art 1] Patent Publication No. 3815537B is incorporated herein by reference.
However, when two pairs of four lock gears comprising a pair of first lock gears and a pair of second lock gears are employed as the above-mentioned lock gears, it is difficult to set the shape of the cam for biasing each of the lock gear radially and outwardly and high dimensional accuracy is required.